To identify novel genes that may contribute to insulin resistance, we examined skeletal muscle gene expression profiles in non-diabetic full-blooded Pima Indians using 1) human oligonucleotide microarrays containing 6800 genes and 35000 expressed sequence tags (ESTs), and 2) differential display PCR. We have also performed gene expression profiling in skeletal muscle and adipocyte samples from selected insulin resistant and insulin sensitive Swedish subjects in collaboration with Dr. Ulf Smith (Sahlgrenska University Hospital, Sweden)and Dr. Samuel Cushman (NIDDK). We are currently analyzing the data. The potential roles of the differentially expressed genes/ESTs in insulin resistance will be evaluated by examining 1) their functions in relevant metabolic pathways, and additionally for Pima samples: 2) their chromosomal locations relative to peaks of linkage to insulin action and diabetes in a genome-wide scan in the Pima population. Skeletal muscle expression levels of selected genes will be further investigated using real-time PCR in a larger group of subjects. Previous studies have indicated strong correlations between biochemical characteristics of primary cultured skeletal muscle cells and clinical parameters of the donors. To determine which of the differentially expressed genes in muscle tissue of insulin resistant vs. insulin sensitive subjects may be primary, rather than secondary abnormalities, we propose also to compare the gene profiles of the cognate cultured myoblasts and myotubes. Similar comparisons will be made to identify obesity susceptibility genes using freshly isolated adipocytes and cultured pre-adipocytes from lean and obese Pima Indians.